It is known to employ relatively high-speed AC motors as one of the primary drivers in power train and transmission design for hybrid or electric type power trains. These types of power trains, especially for use with heavy-duty earthmoving machines, for example, still require gear combinations between the power source and the wheel, typically in the form of a final drive assembly primarily for the purpose of speed reduction. These final drive assemblies require the capability of transferring significant torques in addition to transforming high electric motor shaft speed to a substantially slower axle speed.
Final drives are commonly employed on large earth working machines, such as mining dump trucks for example and typically have at least a pair of driven wheels which are rotatably mounted upon corresponding axle housings or spindles. Each wheel may employ a final drive reduction gear train, such as a double-reduction planetary arrangement, drivingly connected with a cylindrical final drive adapter that partially, if not fully, surrounds the final drive ring gear.
Power to drive such machines is commonly provided by an internal combustion engine which urges rotation of drive axles, provided by the machine, either through a mechanical transmission and differential arrangement or through generation of electrical power to operate electric motors coupled with the drive axles.
As machines increase in size to accommodate larger payloads, the need for more robust drive train components arises, which typically means the use of larger components. For example, it is desirable in trucks which use a planetary final drive to utilize as large a ring gear as reasonably possible to reduce stress on the drive train and increase component life.
Known final drive gear train sets have utilized a Ravigneaux gear set for speed modification between an input an output, however these types of gear sets are complicated (including clutches and multiple gear sets) and are typically expensive to implement. Moreover, these aforesaid gear types often still require additional speed reduction devices attached therewith to attain desirable speed reduction resulting in expensive, complicated and large units.
Another type of final drive assembly is disclosed by U.S. Pat. No. 4,437,530 issued to De Young et al. on Mar. 20, 1984. A pair of coaxially positioned gear sets, provided within a wheel assembly, provide speed reduction between the input and the wheel assembly. Although less complex and likely less expensive than the Ravigneaux gear set, additional speed modification may be necessary to attain desirable rotational speed reduction performance.
The present invention is directed to overcoming one or more of the problems described above.